I. Field of Invention
The present invention concerns a microfluidic device that has inner surfaces with chemical surface characteristics that have been introduced using gas plasmas having one or more organic precursor compounds.
II. Related Art
A number of different techniques for modifying substrate surfaces are well known. One common method is to subject a substrate surface, for instance made in plastics, to various forms of plasma treatment (Chan et al., Surface Science Reports 24 (1996) 1–54; and Garbassi et al., Polymer Surfaces—From Physics to Technology, John Wiley (1998) 238–241). This is done in a plasma reactor, which is a vacuum vessel containing a gas at low pressure (typically 10 to 1000 mTorr). When a high frequency electric excitation field is applied over the reactor, a plasma (also called glow discharge) is formed, containing reactive species like ions, free radicals and vacuum-UV photons. These species may react with other species and/or with the surface and cause a chemical modification of the substrate surface with properties depending on the nature of the gas and on the plasma parameters. Gases like oxygen and argon are typically used for hydrophilization and/or adhesion improvement on plastics, while vapors of organic precursor compounds can be used to apply thin coatings for a number of different purposes (Yasuda, Plasma Polymerization, Academic Press 1985).
Previously, vapors of organic precursor compounds have been used to produce surfaces that are wettable by aqueous liquids but the hydrophilicity has been moderate and not utilized to facilitate transport of aqueous liquids, in microchannels. In some cases, the primary goal has been to introduce coats that have a low non-specific adsorption, for instance of proteins and/or other biopolymers and/or other bioorganic molecules. See for instance discussions U.S. Pat. No. 5,153,072 (Ratner et al.), U.S. Pat. No. 5,002,794 (Ratner et al.), U.S. Pat. No. 6,329,024 (Timmons et al.), U.S. Pat. No. 5,876,753 (Timmons et al.), EP 896035 (Timmons et al.). Strictly hydrophobic surfaces have also been produced. See for instance U.S. Pat. No. 5,171,267 (Ratner et al.).
WO 0056808 (Ocklind, Larsson and Dérand, Gyros AB) describes microfluidic devices comprising hydrophilic microchannel structures defined between two essentially planar substrates that are apposed. Before being apposed the surface of at least one of the substrates has been hydrophilized in gas plasma, which comprises a non-polymerizable gas. The surfaces obtained are hydrophilic and can be coated subsequent to gas plasma treatment in order to introduce further functionalities.
WO 9958245 (Larsson et al.) and WO 97 21090 (Mian et al.) are examples of publications that in general terms suggest microfluidic devices in which the inner surfaces of the microchannel structures have been made hydrophilic by gas plasma treatment, coating of hydrophobic surfaces with hydrophilic polymer, etc.